1. Field of the Invention
The present invention relates to an exciter directly attached to a board member for vibrating the board member and a speaker utilizing this exciter. In particular, the present invention relates to an exciter where heat produced due to the vibration is efficiently dissipated and dust is protected against when the exciter is attached to a board member and is driven as a source of vibration of a speaker and to a speaker designed to eliminate any difference in sound quality occurring in the speaker due to restrictions of the attachment surface of a board member when attaching an exciter to a board member.
2. Description of the Related Art
In the past, in stereo systems, PCs, mobile phones, and other electronic apparatuses, speakers have been used to output audio information from various media. In such speakers, vibration boards for emitting sound are attached to exciters supplied with the drive signals for audio output. These vibration boards have horn shapes specially designed for such speakers. For example, the vibration boards have voice coils of exciters affixed to them. Sound is output by these voice coils vibrating by magnetic circuits.
Such speakers are also used to reproduce music or speech in vehicles, for example, the compartments of passenger cars. These speakers are for example built into the doors of the front seats or are placed on the rear trays. Usually a plurality of speakers are arranged attached to at least one of the front seat and rear seat sides.
In addition to arranging speakers for audio reproduction inside the front seat doors or on the rear trays, arrangement of speakers including direct drive exciters at the ceiling panels of the compartments has for example been disclosed in Japanese Utility Model Publication (Kokai) No. 6-45865.
When attaching usual speakers in a compartment, there are restrictions on the positions of attachment of the speakers. Speakers of too large nominal sizes cannot be used. To deal with this, car-mounted speakers using exciters directly attach the exciters to the ceiling panels and use the ceiling panels as vibration boards to form speakers instead of the conventional speakers having large nominal sizes.
In addition to such exciters, various exciters for board direct drive use able to be used for car-mounted speakers built into ceiling panels etc. have been proposed. An exciter able to be used as a car-mounted speaker is disclosed for example in Japanese Unexamined Patent Publication (Kokai) No. 2003-143690.
To operate such a board direct drive exciter as a speaker, a drive signal is supplied to a coil. The supply of this drive signal, however, causes the coil to generate heat. Even with a usual voice coil type speaker, in the same way as the case of an exciter for board direct drive use, there is a space region inside the voice coil. The heat generated by the voice coil may cause heat buildup in the space region. In the case of such a voice coil type speaker, since the amplitude of vibration of the voice coil is large, it is possible to discharge heat built up in the space region by air convection, so the parts, including the voice coil, will not become high in temperature.
However, in the case of an exciter for board direct drive use, since the space region in the bobbin is communicated with the outside space and the amplitude of the vibration is comparatively small due to the structure for driving vibration, depending on the vibration, the air convection occurring in the space region will be weak and the heat built up will not be able to be exhausted completely. Therefore, the problem of the exciter itself becoming high in temperature will arise and measures will become necessary for preventing deformation due to the heat of the coupler member. Measures become necessary such as employment of a heat resistant material for the interior panel. As a result, the problem of the cost swelling arises.
Further, when forming a speaker by directly attaching an exciter of the type disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 6-45865 etc. to the interior panel of a vehicle, the space region formed at the inside of the bobbin around which the coil is wound is communicated with the outside space. Therefore, there is the problem of dust, dirt, etc. entering the space region from the outside space. Further, dust, dirt, etc. ends up depositing in the clearances formed by the inner yoke, coil bobbin, or outer yoke forming the exciter. These clearances are filled with dust, dirt, etc. As a result, the air convection due to the vibration occurring at the time of coil drive is weakened or inhibited, so the dissipation of heat generated is inhibited or abnormal noise is generated or disconnection occurs due to rubbing of the voice coil.
On the other hand, speaker are used for reproducing music or speech in the compartment of a vehicle such as a passenger car. These speakers are for example embedded in the doors of the front seats or placed on the rear tray. A plurality of speakers are attached to and arranged at least at one of the front seat side and rear seat side in usual practice.
When attaching usual speakers to the inside of a compartment, there are restrictions on the positions of attachment of the speakers. To deal with the fact that a speaker having too large a nominal size cannot be used, in the audio system disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 6-45865, a large speaker directly attached to the ceiling panel is used instead of a conventional speaker having a large nominal size.
In such an audio system, front speakers are embedded in the doors of the front seat among the front seats including the driver's seat and the rear seats in the compartment of a passenger car, while a rear speaker is placed on the rear tray of the rear seats. The ceiling panel of the passenger car is generally comprised of an exterior panel and a ceiling panel. The ceiling panel is provided near its center with an exciter for board direct drive use, whereby a speaker is formed. This ceiling panel is usually formed by a material such as urethane or polypropylene foam, so the ceiling panel itself can perform the role of a vibration board of the speaker.
The speaker utilizing the exciter for board direct drive use can form a speaker by directly attaching the exciter to any board member having a suitable area. Since the board member serves as a vibration board, no special vibration board is needed. For example, it is possible to form a car-mounted speaker by a magnetic circuit, frame, vibration board, etc., arrange it near the ceiling of a passenger car, and attach it so that the aperture of the speaker is near the ceiling side, so it is possible to reproduce the medium and high sound regions. By arranging the speaker near the ceiling, it is possible to enhance the feeling of closeness of the sound field and thereby possible to form a better sound field in the compartment.
Note that when employing speakers attaching exciters to an interior panel of a passenger car to form a stereo reproduction space in the compartment of the passenger car, two exciters may be directly attached on the interior panel of the ceiling of the compartment a predetermined distance apart to the left and right.
Here, the pair of exciters are thereby attached to a single common interior panel. As a result of using part of the interior panel as a vibration board, if the interval of arrangement of the pair of exciters is too narrow, even if the exciters driven by the stereo signal are attached independently, the stereo feeling is impaired when listening and the effect becomes monaural.
As will be understood from the state by which this vibration energy is transmitted, to form a stereo reproduction space, the pair of exciters have to be attached to the interior panel a predetermined distance apart. Further, the vibration energy is transmitted over a wider range the flatter the surface, so to obtain the desired sound properties, flatness is required. If considering the formation of an optimal stereo space in the compartment, the positions for attaching the pair of exciters are naturally restricted to a certain range in the front-rear direction of the compartment.
However, depending on the vehicle where a pair of exciters are to be directly attached to the interior panel to try to form the stereo reproduction space, even if the same model of vehicle, the interior etc. will sometimes differ depending on the specifications etc. For example, the same model will include cases of no sunroof and of sunroofs.
Therefore, if trying to form the optimal stereo reproduction space in the compartment, since the shape of the compartment of the same model of vehicle will be the same if the same model, the positions of arrangement of the pair of exciters at the interior panel will be restricted without regard as to the existence of any sunroof. Accordingly, even when a sunroof is provided, the pair of exciters will be attached to the same positions as the case of no sunroof.
However, the range of transmission of vibration energy from the pair of exciters is affected by the sunroof of an interior panel. Therefore, when the same exciters are used, a difference will arise in the sound quality in the stereo reproduction space depending on the sunroof etc.
With a situation where while the same model, a sunroof will cause the sound quality to differ, users purchasing vehicles with sunroofs would complain. If exciters for vehicles with sunroof specifications were developed, those complaints could be eliminated, but there would then be the problem that development of exciters to meet with different specifications of interior panels would cause costs to balloon.
Therefore, in view of these problems, the present invention has as its object the provision of an exciter for board direct drive use designed to improve the air compression rate due to vibration of the space region in a device so as to promote air convection and thereby facilitate dissipation of generated heat and provide dustproofing preventing the entry of dust, dirt, etc. inside the device.
Further, the present invention, in view of the above problem, has as its object the provision of a speaker designed to limit the range of transmission of vibration energy of an exciter even for different specifications of board members forming vibration boards and to utilize an exciter for board direct drive use which enables an exciter having common specifications to be attached to such board members.